Mechanical end face seals have long been used to seal the space between a housing and a rotating shaft which passes through the housing. Such seals usually include a primary ring which has a radial sealing face and is mounted on the shaft by a secondary seal such as an O-ring. In addition, the seal includes a fixed mating ring mounted in the housing. Like the primary ring, the mating ring has a radial sealing surface. The two radial surfaces are biased into sealing engagement.
These seals were developed as a substitute for packing--a braided, flexible material which was stuffed into the space between the shaft and the housing and compressed by a gland plate. Being a substitute for packings, many end face seals were designed with dimensions which would permit their installation in the same space. Thus dimensional, installation and maintenance challenges arose.
Still later, these challenges were magnified by pumps generating higher pressures and exposed to corrosive or toxic liquids. Engineers responded with designs of end face seals in "tandem" or in "double"--often designing them to fit in the same space as the earlier packings. The latest developments are directed to a package seal, e.g. an integral unit mounted on a sleeve to facilitate installation over the shaft and to avoid alignment problems between the seal faces.
As a result of these developments, numerous designs are available--each seal and its parts being dimensioned for a specific size of shaft and housing. Consequently, present seal designs lack versatility. Neither the overall design nor the individual parts can be easily fitted to different shafts and different housings. Moreover, these cartridge designs do not facilitate pretesting, and often have rotating parts which are disposed outside the housing.
An illustration of these designs is depicted in Industrial Sealing Technology, H. H. Buchter, at FIG. 2.48. This illustration depicts double seals mounted on a sleeve, one of the seals extending into the housing and the other exposed outside the housing. Only two parts of the seal (the primary rings) have the same dimensions, and the clearances are such that the seal parts cannot be adapted to fit other shaft sizes.